I was making a cut scene for a game I was making. It involved and npc walking to the character: the npc having an animation whilst it walked to the character. I stored the npc in Replicated First and sent it over to the server - my first mistake. I already knew that Replicated First replicates to the client first, but not back to the server.
I finished the cutscene - I thought - and tested it on the game and it turns out I did things on the client that should've been done on the server and I had to fix it. I cloned the character from Replicated First, on the client, and tried it in Replicated Storage because of how ReplicatedFirst replicates to the client and not back to the server, but doing that didn't fix it. Eventually I fixed it - mostly - and it seemed to work when I stored the npc in Replicated First except the animations wouldn't play.
I asked on the discord multiple times, but never got an answer that worked. Around 9:30 AM to 9:40 AM today I was testing the animation on the local server option on Studio. I was on the server side tab messing with the humanoid as I thought it could be that the Animator wasn't in it(it was) and I was just clicking booleans like sit, jump and platform stand on the studio and then I released...
The animation was playing, but only on the server tab. Turns out if you get something from Replicated First on the client and remotely send it over to the server: Filtering Enabled seems to get flipped around as the server can see it, but not the client. I've seen this happen another time when using PlayerAdded on a local script, because I forgot to change it to a server script.
There's probably an explanation for this, but I wanted to share this with you.